Retrofittable vapor source for vacuum metallizing utilizing spatter reduction means

Abstract

A metal vapor evaporator source is provided that increases productivity of a vacuum plating operation in which it is used by reducing scrap product due to spatter of liquid metal particles from the evaporator to the product, and by reducing spurious metal condensate within the vacuum chamber, the accumulation of which metal condensate is known to increase downtime of the equipment. The former is accomplished by inhibiting the generating of such particles by increasing the total pressure on the pool of molten metal and by physically intercepting many of the spattered particles that are generated despite the increased pressure. The latter is accomplished by partially collimating the beam of metal vapor, a result of intercepting and condensing the stray vapor on a radiant-heat shield that is at a temperature above the melting point of the metal.

I claim: 
     
       1. An evaporation source for use in a source continuous vacuum metal vaporizing process, for providing a metal vapor therefor, said evaporation source comprising: a substantially closed container in the shape of a cylinder having an axis, having a refractory cylindrical wall with an inner and an outer surface thereof, and having a first and a second refractory end closure, said container being disposed with said axis thereof substantially in a horizontal orientation and said container adapted by means of having at least one through passage in said wall to allow the passage of a directed beam of said metal vapor;   said container being adapted to allow the feeding of a substantially continuous metal wire into said container by way of a said at least one through passage, thereby to supply to said container metal that may, when heated sufficiently, melt to form a pool of liquid metal therein and ultimately to vaporize and exit said container by way of a said at least one through passage;   means to heat said container and said metal to temperatures suitable for converting said metal to a liquid and then to a vapor;   said means to heat said container being adapted to be held in mechanical and electrical contact in the "arm chair" connections of the prior art, thereby making said evaporation source retrofittable into prior art vapor plating equipment; and   wherein said wall reduces particulate spatter and extraneous vapor condensation during operation of said evaporation source.   
     
     
       2. The evaporation source of claim 1 with the added feature of having the area of said through passage sufficiently small, of a width of approximately 1/4 inch to 5/8 so as to restrict passage of metal vapor, thereby to increase pressure within said container sufficently to effect an increase in the temperature at which spattering of particulate metal begins from said pool of liquid metal. 
     
     
       3. The evaporation source of claim 1 wherein said means to heat said container comprises a resistance heating element positioned axially through said container, passing through close-fitting holes through said first and second end closures and adapted by means of end blocks for mechanical and electrical connection to said "arm chair" connections of the prior art. 
     
     
       4. The evaporation source of claim 3 wherein said resistance heating element comprises a graphite rod. 
     
     
       5. The evaporation source of claim 4 wherein said graphite rod has, on a significant portion thereof, a protective coating of pyrolytically deposited boron nitride (BN). 
     
     
       6. The evaporation source of claim 1 wherein said means to heat said container comprises a medially bifurcated resistance heating element upon which said container rests in direct contact. 
     
     
       7. The evaporation source of claim 6 wherein said resistance heating element is made of graphite. 
     
     
       8. The evaporation source of claim 1 further comprising a thermal radiation shield in the shape of a curved plate surrounding said container and spaced away therefrom, said shield being open on the bottom and having a through passage in registry with said through passage of said container, thereby to partially collimate said beam of metal vapor. 
     
     
       9. The evaporation source of claim 8 wherein the material of said thermal radiation shield is selected from the group consisting of graphite, flexible graphite (i.e., compressed vermicular graphite), silicon nitride, silicon carbide, and titanium diboride. 
     
     
       10. The evaporation source of claim 9 wherein the material of said thermal radiation shield is silicon carbide. 
     
     
       11. The evaporation source of claim 1 wherein the refractory material of said refractory cylinder wall is selected from the group consisting of aluminum nitride, boron nitride, silicon nitride, titanium diboride, and mixtures thereof. 
     
     
       12. The evaporation source of claim 11 wherein the refractory material is titanium diboride. 
     
     
       13. The evaporation source of claim 1 wherein the refractory material of said refractory end closures is aluminum nitride. 
     
     
       14. The evaporation source of claim 1 wherein the refractory material of said refractory end closures is boron nitride.